Estrogens are a group of female hormones essential for the reproductive process and for the development of the uterus, breasts, and other physical changes associated with puberty. Estrogens have an effect on various tissues throughout a woman's body, not only those involved in the reproductive process, such as the uterus, breasts, and external genitalia, but also tissues in the central nervous system, bones, the liver, skin, and the urinary tract. The ovaries produce most of the estrogens in a woman's body.
Menopause is defined as the permanent cessation of menses due to loss of ovarian follicular function and the near complete termination of estrogen production. The midlife transition of menopause is characterized by a decrease in estrogen that provokes both short-term and long-term symptoms with the vasomotor, urogenital, cardiovascular, skeletal and central nervous systems, such as hot flushes, urogenital atrophy, increased risk of cardiovascular disease, osteoporosis, cognitive and psychological impairment, including an increased risk of cognitive disorders and Alzheimer's disease (AD).
Seventy-five percent of all women experience some occurrence of vasomotor symptoms associated with the onset of menopause such as body sweating and hot flushes. These complaints may begin several years before menopause and in some women may continue for more than 10 years, either relatively constant, or as instant attacks without a definable, provoking cause.
Urogenital symptoms associated with the onset of menopause involving the vagina include a sensation of dryness, burning, itching, pain during intercourse, superficial bleeding and discharge, along with atrophy and stenosis. Symptoms involving the urinary tract include a burning sensation during urination, frequent urgency, recurrent urinary tract infections, and urinary incontinence. These symptoms have been reported to occur in up to 50% of all women near the time of menopause and are more frequent a few years after menopause. If left untreated, the problems can become permanent.
Heart attack and stroke are major causes of morbility and mortality among senior women. Female morbility from these diseases increases rapidly after menopause. Women who undergo premature menopause are at greater coronary risk than menstruating women of similar age. The presence of serum estrogen has a positive effect on serum lipids. The hormone promotes vasodilation of blood vessels, and enhances the formation of new blood vessels. Thus the decrease in serum estrogen levels in postmenopausal women results in an adverse cardiovascular effect. Additionally, it is theorized that differences in the ability of blood to coagulate may account for the observed difference in the occurrence of heart disease before and after menopause.
The skeleton is under a continuous process of bone degeneration and regeneration in a carefully regulated interaction among the bone cells. These cells are directly affected by estrogen. Estrogen deficiency results in a loss of bone structure, and decrease in bone strength. Rapid loss of bone mass during the year immediately following menopause leads to postmenopausal osteoporosis and increased risk of fracture.
Estrogen deficiency is also one of the causes for the degenerative changes in the central nervous system and may lead to Alzheimer's disease (AD) and a decline of cognition. Recent evidence suggests an association between estrogen, menopause and cognition. More particularly, it has been reported that estrogen replacement therapy and the use of estrogen in women may prevent the development of AD and improve cognitive function.
Hormone replacement therapy (HRT)—more specifically estrogen replacement therapy (ERT)—is commonly prescribed to address the medical problems associated with menopause, and also to help hinder osteoporosis and primary cardiovascular complications (such as coronary artery disease) in both a preventive and therapeutical manner. As such, HRT is considered a medical therapy for prolonging the average life span of postmenopausal women and providing a better quality of life.
ERT effectively relieves the climacteric symptoms and urogenital symptoms and has shown some benefits in the prevention and treatment of heart disease in postmenopausal women. Clinical reports have shown that ERT lowered heart attack rates and mortality rates in populations that received ERT versus similar populations not on ERT. ERT initiated soon after menopause may also help maintain bone mass for several years. Controlled investigations have shown that treatment with ERT has a positive effect even in older women up to 75 years of age.
However, there are numerous undesirable effects associated with ERT that reduce patient compliance. Venous thromboembolism, gallbladder disease, resumption of menses, mastodynia, and a possible increased risk of developing uterine and/or breast cancer are the risks associated with ERT. Up to 30% of women who are prescribed ERT do not fill the prescription, and the discontinuation rate for ERT is between 38% and 70%, with safety concerns, and adverse effects (bloating and break-through bleeding) the most important reasons for discontinuation.
A new class of pharmacological agents known as Selective Estrogen Receptor Modulators or SERMs have been designed and developed as alternatives for HRT. Raloxifene, a nonsteroidal benzothiophere SERM is marketed in the US and Europe for the prevention and treatment of osteoporosis under the trademark of Evista®. Raloxifene has been shown to reduce bone loss and prevent fracture without adversely stimulating endometrial and mammary tissue, though raloxifene is somewhat less efficacious than ERT for protecting against bone loss. Raloxifene is unique and differs significantly from ERT in that it does not stimulate the endometrium and has the potential for preventing breast cancer. Raloxifene has also demonstrated beneficial estrogen agonist effects on cardiovascular risk factors, more specifically through a rapid and sustained decrease in total and low-density lipoprotein cholesterol levels in patients treated with raloxifene. In addition, raloxifene has been shown to reduce plasma concentration of homocysteine, an independent risk factor for atherosclerosis and thromboembolic disease.
However, raloxifene has been reported to exacerbate symptoms associated with menopause such as hot flushes and vaginal dryness, and does not improve cognitive function in senior patients. Patients taking raloxifene have reported higher rates of hot flashes compared with either placebo or ERT users and more leg cramps than placebo users, although women who took ERT had a higher incidence of vaginal bleeding and breast discomfort than raloxifene or placebo users.
As yet, neither raloxifene nor any of the other currently available SERM compounds has been shown to have the ability to provide all the benefits of currently available ERT, such as controlling postmenopausal syndrome and preventing AD, without causing adverse side effects such as increasing risk of endometrial and breast cancer and bleeding. Thus there exists a need for compounds which are selective estrogen receptor modulators and which provide all of the benefits of ERT while also addressing the vasomotor, urogenital and cognitive disorders or conditions associated with the decrease in systemic estrogen associated with menopause.
Androgens are the anabolic steroid hormones of animals, controlling muscle and skeletal mass, the maturation of the reproductive system, the development of secondary sexual characteristics and the maintenance of fertility in the male. In women, testosterone is converted to estrogen in most target tissues, but androgens themselves may play a role in normal female physiology, for example, in the brain. The chief androgen found in serum is testosterone, and this is the effective compound in tissues such as the testes and pituitary. In prostate and skin, testosterone is converted to dihydrotestosterone (DHT) by the action of 5α-reductase. DHT is a more potent androgen than testosterone because it binds more strongly to the androgen receptor.
Like all steroid hormones, androgens bind to a specific receptor inside the cells of target tissues, in this case the androgen receptor. This is a member of the nuclear receptor transcription factor family. Binding of androgen to the receptor activates it and causes it to bind to DNA binding sites adjacent to target genes. From there it interacts with coactivator proteins and basic transcription factors to regulate the expression of the gene. Thus, via its receptor, androgens cause changes in gene expression in cells. These changes ultimately have consequences on the metabolic output, differentiation or proliferation of the cell that are visible in the physiology of the target tissue.
Although modulators of androgen receptor function have been employed clinically for some time, both the steroidal (Basaria, S., Wahlstrom, J. T., Dobs, A. S., J. Clin Endocrinol Metab (2001), 86, pp 5108-5117; Shahidi, N. T., Clin Therapeutics, (2001), 23, pp 1355-1390), and non-steroidal (Newling, D. W., Br. J. Urol., 1996, 77 (6), pp 776-784) compounds have significant liabilities related to their pharmacological parameters, including gynecomastia, breast tenderness and hepatoxicity. In addition, drug-drug interactions have been observed in patients receiving anticoagulation therapy using coumarins. Finally, patients with aniline sensitivities could be compromised by the metabolites of non-steroidal antiandrogens.
Non-steroidal agonists and antagonists of the androgen receptor are useful in the treatment of a variety of disorders and diseases. More particularly, agonists of the androgen receptor could be employed in the treatment of prostate cancer, benign prostatic hyperplasia, hirsutism in women, alopecia, anorexia nervosa, breast cancer and acne. Antagonists of the androgen receptor could be employed in male contraception, male performance enhancement, as well as in the treatment of cancer, AIDS, cachexia, and other disorders.
Progesterone plays a major role in reproductive health and functioning. Its effects on, for example, the uterus, breast, cervix and hypothalamic-pituitary unit are well established. The actions of progesterone as well as progesterone antagonists are mediated by the progesterone receptor (PR). In the target cell, progesterone produces a dramatic change in confirmation of the PR that is associated with transforming the PR from a non-DNA binding form to one that will bind to DNA. This transformation is accompanied by a loss of associated heat shock proteins and dimerization. The activated PR dimmer then binds to specific DNA sequences within the promotor region of progesterone responsive genes. The agonist-bound PR is believed to activate transcription by associating with coactivators, which act as bridging factors between the receptor and the general transcription machinery. This is followed by increases in the rate of transcription producing agonist effects at the cellular and tissue levels. These progesterone receptor ligands exhibit a spectrum of activity ranging from pure antagonists to mixed agonists/antagonists.
In 1982, the discovery of compounds that bind to the progesterone receptor, antagonize the effects of progesterone receptor and antagonize the effects of progesterone was announced. Although compounds such as estrogens and certain enzyme inhibitors can prevent the physiological effects of endogenous progesterone, the term “antiprogestin” is confined to those compounds that bind to the progestin receptor. A report from the Institute of Medicine (Donaldson, Molly S.; Dorflinger, L.; Brown, Sarah S.; Benet, Leslie Z., Editors, Clinical Applications of Mifepristone (RU 486) and Other antiprogestins, Committee on antiprogestins: Assessing the science, Institute of medicine, National Academy Press, 1993) summarized a number of medical conditions related to the effect of antiprogestins. In view of the pivotal role that progesterone plays in reproduction, it is not surprising that antiprogestins could play a part in fertility control, including contraception, menses induction and medical termination of pregnancy, but there are many other potential uses that have been supported by small clinical or preclinical studies, such as labor and delivery; treatment of uterine leiomyomas (fibroids), treatment of endometriosis; HRT; breast cancers; male contraception, etc.
The effects and uses of progesterone agonists have been well established. In addition, it has been recently shown that certain compounds structurally related to the known antiprogestins have agonist activity in certain biological systems (e.g., the classical progestin effects I the estrogen-primed immature rabbit uterus; cf. C. E. Cook et al., Life Sciences, 52, 155-162 (1993)). Such compounds are partial agonists in human cell-derived receptor systems, where they bind to a site distinct from both the progestin and antiprogestin sites (Wagner et al., Proc. Natl. Acad. Sci., 93, 8739-8744 (1996)). Thus the general class of antiprogestins can have subclasses, which may vary in their clinical profiles.
Compounds which mimic some of the effects of progesterone (agonists), antagonize these effects (antagonists, antiprogestins) or exhibit mixed effects (partial agonists or mixed agonist/antagonist), known as progesterone receptor modulators (PRMs) can be useful in treating a variety of disease states and conditions. PR agonists have been used in female contraceptives and in postmenopausal hormone therapy. Recent studies in women and non-human primates show that PR antagonists may also have potential as contraceptive agents and for the treatment of various gynecological and obstetric diseases, including fibroids, endometriosis and, possibly, hormone-dependent cancers. Clinically available PR agonists and antagonists are steroidal compounds and often cause various side effects due to their functional interaction with other steroid receptors. Recently, numerous receptor-selective non-steroidal PR agonists and antagonists have emerged. Non-steroidal PR antagonists, being structurally distinct from the steroid class, may have greater potential for selectivity against other steroid receptors.